A technique of manufacturing a semiconductor device, provided with a semiconductor element such as a transistor essentially includes a technique of forming a fine pattern for enhancing integration. Recently, the improvement in overlay accuracy between layers has become significant with the further microfabrication of the pattern.
A fine body pattern (device pattern) is not resolved by an optical measuring apparatus. Therefore, the overlay displacement amount between layers has been measured by using an alignment mark formed separate from the device pattern. During the measurement of the overlay displacement amount described above, the overlay displacement amount measured by using the alignment mark and the overlay displacement amount of the body pattern (circuit pattern) might be different from each other with the more microfabrication of the pattern.
A method of measuring the overlay displacement amount by using an SEM (Scanning Electron Microscope) having high resolution has been developed. This measuring method includes two methods, which are a method of directly measuring the overlay displacement amount and a method of indirectly measuring the overlay displacement amount.
In the former method, after a lower layer and an upper layer are both formed, the overlay between the body patterns is directly measured by using an SEM image captured from above the upper layer. In this method, an electron beam has to pass through the upper layer. Therefore, it is difficult to set the observation condition of the SEM, and further, a substrate is significantly damaged.
In the latter method, the positional displacement amount of the alignment mark from the body pattern after the lower layer is formed and the same positional displacement amount after the upper layer is formed are respectively measured by using the SEM image. The overlay displacement amount between the alignment marks measured by the optical measuring apparatus is added to the respective positional displacement amounts, whereby the overlay displacement amount of the body patterns is indirectly measured.
In the latter method, the positional relationship between the alignment mark and the body pattern cannot be measured with high accuracy, since the positional relationship between the alignment mark and the body pattern is changed due to the thermal expansion of the substrate. Accordingly, the latter method entails a problem that the overlay displacement amount between the upper layer and the lower layer cannot accurately be measured. Consequently, an accurate measurement of the overlay displacement amount between the upper layer and the lower layer has been demanded.